This invention relates to an optical transport apparatus and an optical transport system and, in particular, relates to an optical transport apparatus and an optical transport system having wavelength division multiplexing and optical add-drop capabilities.
Recent drastic increase in data traffic represented by the Internet is propelling expansion of transport capacity in a communication network. Such expansion of transport capacity is achieved by time division multiplexing technology and optical wavelength division multiplexing technology. Currently, point-to-point wavelength division multiplexing systems are in practical use, achieving long distance transport over several-hundred kilometers with transmitters at 10 Gbit/s for a channel, several to dozens of channels of wavelengths multiplexed on a single optical fiber, and optical amplifiers or regenerators.
In order to meet increasing demand for larger transport capacity, further cost effectiveness, and more diverse services in the future, optical ring networks are being studied that annularly connect communication nodes. In addition, for more flexible route selection, optical mesh networks are being studied that connect communication nodes like meshes.
Optical transport apparatuses used in the optical ring networks are called optical add-drop multiplexers (OADMs). Optical transport apparatuses used in the optical mesh networks are called optical cross-connects (OXCs).
These optical transport apparatuses can pass optical signals through the nodes without converting the optical signals into electric signals; consequently, an overall network can be attained inexpensively. In addition, simpler operation can be achieved by a network management system that remotely and unitarily manages the nodes. Furthermore, easier management and speedier establishment of an end-to-end path from a starting point to a terminal point of a line can be expected through cooperation of supervisory controllers in individual nodes.
The OADMs and OXCs use optical switches to select either add-drop or letting through of optical signals and to select routes. Currently, some technologies are known to provide such optical switches, for example, semiconductor switches and LiNO3 switches utilizing changes in refractive index caused by application of electric field to the material, and planar lightwave circuit (PLC) switches utilizing changes in refractive index caused by application of heat to the material.
In addition to these switches, also known are optical switches with moving parts that move optical fibers or lenses with electric magnets, micro-electro-mechanical system (MEMS) switches that control micro mirrors, which are produced by a semiconductor technology, by statistic electricity, and liquid crystal optical switches that select transmission or reflection of optical signals by changing voltage to apply to the liquid crystal.
As an applied technology of the MEMS or the liquid crystal technologies, wavelength selective switches (WSSs) which have wavelength division multiplexing functionality in addition to selecting functionality are known. For example, JP 2006-140598A discloses an optical transmission apparatus including WSSs.
JP 2006-140598A discloses that an optical route switching means selects signal light of one or more wavelengths from wavelength division multiplexing (WDM) light received from any one of the input ports to output it from any of the output ports. According to JP 2006-140598A, this configuration achieves a change of route from a route for signal light of intended wavelengths included in WDM light to different routes without demultiplexing the WDM light by individual wavelengths like a conventional technique; consequently, considerable number of ports required for the optical route switching means can be reduced.
JP 2008-60773A discloses an optical transmission apparatus in which the output direction of an added optical signal is not fixed to allow discretional selection of the output direction. According to JP 2008-60773A, the optical transmission apparatus has optical add-drop functionality to add/drop an optical signal of any wavelength to an intended direction to/from any add-drop unit; consequently, the apparatus can easily cope with increase or decrease in the number of directions and the number of wavelengths while achieving simpler and more compact apparatus structure.